A stent is an elongated device used to support an intraluminal wall. In the case of a stenosis, a stent provides an unobstructed conduit for blood in the area of the stenosis. Such a stent may also have a prosthetic graft layer of fabric or covering lining the inside or outside thereof, such a covered stent being commonly referred to in the art as an intraluminal prosthesis, an endoluminal or endovascular graft (EVG), or a stent-graft. As used herein, however, the term “stent” is a shorthand reference referring to a covered or uncovered such stent.
A stent may be used, for example, to treat a vascular aneurysm by removing the pressure on a weakened part of an artery so as to reduce the risk of rupture. Typically, an intraluminal stent is implanted in a blood vessel at the site of a stenosis or aneurysm endoluminally, i.e. by so-called “minimally invasive techniques” in which the stent, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a stent deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient's skin, or by a “cut down” technique in which the entry blood vessel is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the stent deployment location, the introducer is manipulated to cause the stent to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the stent), whereupon the stent expands to a predetermined diameter in the vessel into the deployment location, and the introducer is withdrawn. Stent expansion may be effected by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Referring now to FIGS. 1A and 1B, there is shown a prior art, pre-loaded stent delivery system 10 for housing and deploying a compressed stent 14. Stent delivery system 10 comprises an outer sheath 12 and a conventional pusher or stabilizer 16 loaded proximal to the stent. As used herein, the term “proximal” refers to the end closer to an access location outside the body whereas “distal” refers to the farther from the access location. Delivery system 10 also typically comprises a catheter tip 20 at the distal end and a pusher handle 25 located at the proximal end outside the body lumen. The catheter tip may be attached to central core 23 that runs through central lumen 22 within pusher 16. Central core 23 may guide the delivery system through the body lumen over a guidewire (not shown) to the area to be repaired, or may be adapted for inflating a balloon (if applicable), and/or for flushing the system. The delivery system may additionally have radiopaque markers at selected locations therein to be used for fluoroscopic guidance of the system through the body lumen.
To deploy stent 14, delivery system 10 is threaded through the body lumen to the desired location for stent deployment. Outer sheath 12 is then retracted, and pusher 16 acts as a stabilizer to keep stent 14 from retracting with the sheath. As outer sheath 12 retracts, stent 14 is exposed and expands into place against the body lumen to be repaired. The stent may be a self-expanding stent, such as a stent made of shape-memory nitinol (nickel-titanium) wire as are well-known in the art, or the stent may require inflation of a balloon to expand it against the walls of the body lumen, as is also well-known in the art.
Regardless of the type of stent or delivery system, the portion of delivery system 10 that houses compressed stent 14 typically has increased mass and rigidity as compared to the rest of delivery system 10. Thus, referring now to FIG. 2, when introducing delivery system 10 through tortuous anatomy, kinking of the delivery system may occur in region 17 of the system where pusher 16 and stent 14 interface, due to the rigidity of both the stent and the pusher. Kinking along kink angle “a” may develop as a result of the rigidity of compressed stent 14, whereas kinking along kink angle “b” may develop as a result of the rigidity of pusher 16. The resulting kink angle a+b is therefore dependent upon the material properties of both the compressed stent 14 and pusher 16. Similar kinking may also occur in region 18 where stent 14 and tip 20 interface.
Such kinking may prevent or hamper proper deployment of stent 14 because creases 15 that develop where sheath 12 is bent may prevent retraction of the sheath. Such creases 15 present a problem not only where stent 14 is intended for deployment in the tortuous portion of the body lumen, but also may persist even after the delivery system 10 is ultimately navigated past the tortuous portion of the lumen to a remote deployment site. Also, the discontinuity of the contact surface between stent 14 and pusher 16 could lead to an improper or inaccurate deployment of the stent. Where kinking causes such creases 15 in sheath 12 that prevent deployment, delivery system 10 must be retracted from the body and discarded, and the introduction process must start again with a new introducer. Thus, there is a need in the art to prevent such kinking in stent delivery systems.